1. Field of the Invention
The present invention relates to an exchange coupling film comprising an antiferromagnetic layer and a ferromagnetic layer, in which the magnetization vector of the ferromagnetic layer is oriented in a particular direction by an exchange coupling magnetic field generated at the interface between the antiferromagnetic layer and the ferromagnetic layer. The present invention is particularly directed to an exchange coupling film having a strong exchange coupling magnetic field, a magnetoresistive element (spin valve thin-film element or AMR element) employing the exchange coupling film, and a thin-film magnetic head incorporating the magnetoresistive element.
2. Description of the Related Art
A spin-valve thin-film magnetic head is a type of giant magnetoresistive element (GMR) which utilizes the giant magnetoresistive effect. The spin-valve thin-film magnetic head detects a recorded magnetic field from a recording medium such as a hard disk.
The spin-valve thin-film magnetic head is preferred for its relatively simple structure compared to other GMR elements and its ability to change the resistance in response to a weak magnetic field.
The simplest type of spin-valve thin-film magnetic head comprises an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic interlayer, and a free magnetic layer.
The antiferromagnetic layer and the pinned magnetic layer are in contact with each other. An exchange anisotropic magnetic field generated at the interface between the antiferromagnetic layer and the pinned magnetic layer puts the magnetization vector of the pinned magnetic layer into a single domain state, thus pinning the magnetization vector.
The magnetization vector of the free magnetic layer is oriented in a direction substantially orthogonal to the magnetization vector of the pinned magnetic layer by bias layers formed on two sides of the free magnetic layer.
The antiferromagnetic layer is typically composed of an Fe—Mn alloy, a Ni—Mn alloy, or a Pt—Mn alloy. The Pt—Mn alloy is particularly preferable since this alloy has a high blocking temperature, excellent corrosion resistance, and other advantageous features.
The inventors have found that even when the PtMn alloy is used in the antiferromagnetic layer, there are some instances where an exchange coupling magnetic field generated between the antiferromagnetic layer and the pinned magnetic layer has a reduced intensity.
When the antiferromagnetic layer is composed of the PtMn alloy, the disordered lattice of the antiferromagnetic layer can be transformed into an ordered lattice by thermally treating the antiferromagnetic layer and the pinned magnetic layer subsequent to their deposition, so as to generated an exchange coupling magnetic field.
However, when the atoms of the antiferromagnetic material constituting the antiferromagnetic layer and the atoms of the soft magnetic material constituting the pinned magnetic layer exhibit a one-to-one correspondence (lattice matching) at the interface between the antiferromagnetic layer and the pinned magnetic layer, the transformation into an ordered lattice does not occur properly in the antiferromagnetic layer. As a result, it becomes impossible to obtain an increased exchange coupling magnetic field.
The above-described lattice matching is considered to occur when the crystal orientations of the antiferromagnetic layer and the pinned magnetic layer are coincident with each other at the interface thereof. An example of such an instance is when the one of the {111} planes of the antiferromagnetic layer is preferentially aligned parallel to the interface with the pinned magnetic layer at the same time one of the {111} planes of the pinned magnetic layer is preferentially aligned in a direction parallel to the above-described interface.